Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual conferência anterior está associada à escola Penn?
 ###Tabelas: CREATE TABLE current_members (current_members_id AUTO_INCREMENT PRIMARY KEY, School VARCHAR, Location VARCHAR, Mascot VARCHAR, County VARCHAR, Enrollment IHSAA Class VARCHAR, Joined INT, Previous Conference VARCHAR) CREATE TABLE southern_railway_batch (southern_railway_batch_id AUTO_INCREMENT PRIMARY KEY, BRNo. INT, SRNo. VARCHAR, Name VARCHAR, Builder VARCHAR, Whenbuilt VARCHAR, Withdrawn VARCHAR) CREATE TABLE us_ratings (us_ratings_id AUTO_INCREMENT PRIMARY KEY, # INT, Airdate VARCHAR, Episode VARCHAR, Rating VARCHAR, Share INT, Rating/Share (18–49) VARCHAR, Viewers (millions) VARCHAR, Rank (Timeslot) INT, Rank (Night) INT) CREATE TABLE season-by-season (season-by-season_id AUTO_INCREMENT PRIMARY KEY, Season VARCHAR, Division VARCHAR, Finish VARCHAR, Wins VARCHAR, Losses VARCHAR, Pct. VARCHAR) CREATE TABLE season_to_season (season_to_season_id AUTO_INCREMENT PRIMARY KEY, Season INT, Level VARCHAR, Division VARCHAR, Administration VARCHAR, Position VARCHAR)  
SELECT Previous Conference FROM current_members WHERE School = penn